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Idelalisib (Zydelig)

Idelalisib (also called Zydelig) is a type of targeted cancer drug. It is a possible treatment for:  

  • chronic lymphocytic leukaemia (CLL)
  • a type of low grade non-Hodgkin lymphoma called follicular lymphoma
  • other types of cancer as part of clinical trials

Idelalisib for chronic lymphocytic leukaemia (CLL) 

You might have idelalisib if your leukaemia has come back after you have had at least one type of treatment. Or you may have it as a first treatment if your CLL has specific gene changes known as 17p deletion or TP53 mutation. 

You usually have it together with another drug called rituximab or ofatumumab.

Idelalisib for follicular lymphoma

You might have idelalisib if your follicular lymphoma comes back after you have had at least 2 other types of treatment. 

How idelalisib works

Idelalisib works by blocking a protein called PI3K inside cancer cells which tell the cancer to grow. Some lymphomas and leukaemia cells have too much PI3K. So by blocking this protein, idelalisib may shrink the cancer or stop it growing for some time. 

Idelalisib is also called a PI3K inhibitor. 

How you have idelalisib

You take idelalisib as a tablet twice a day. You can take it with or without food. 

Don't chew or crush the tablet. You should swallow it whole with a glass of water. 

Taking your tablets or capsules

You must take tablets and capsules according to the instructions your doctor or pharmacist gives you.

You should take the right dose, not more or less.

Talk to your specialist or advice line before you stop taking a cancer drug.

When you have idelalisib

You usually carry on taking idelalisib for as long as it is working and the side effects aren't too bad. 


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

Side effects

We haven't listed all the side effects. It's very unlikely that you will have all of these side effects, but you might have some of them at the same time.

How often and how severe the side effects are can vary from person to person. They also depend on what other treatments you're having. For example, your side effects could be worse if you're also having other drugs or radiotherapy.

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 
  • your side effects aren’t getting any better
  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your doctor or nurse immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

Common side effects

Each of these effects happens in more than 1 in 10 people (10%). You might have one or more of them. They include:

Risk of infection 

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Your doctor may give you antibiotics to prevent infections. 


Contact your advice line if you have diarrhoea, such as if you've had 4 or more loose watery poos (stools) in 24 hours. Or if you can't drink to replace the lost fluid. Or if it carries on for more than 3 days.

Your doctor may give you anti diarrhoea medicine to take home with you after treatment. Eat less fibre, avoid raw fruits, fruit juice, cereals and vegetables, and drink plenty to replace the fluid lost.

Diarrhoea can start up to several months after you start treatment with idelalisib.

Skin changes

Skin problems include a skin rash, dry skin and itching. This usually goes back to normal when your treatment finishes. Your nurse will tell you what products you can use on your skin to help.

High temperature (fever)

You might get a high temperature (fever) for a few hours after having this treatment. Tell your doctor or nurse if you have a fever.

Liver changes

You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.

High levels of cholesterol

Cholesterol is a fatty substance which helps cells in the body to work normally. When the cholesterol level is too high it could have an effect on your heart. You usually have blood tests to check your cholesterol levels.

Occasional side effects

Each of these effects happens in more than 1 in 100 people (1%). You might have one or more of them. They include:

  • inflammation of the lungs (pneumonitis)
  • liver damage

Rare side effects

Very rarely you may develop a severe skin reaction. This may start as tender red patches on the skin which then leads to peeling or blistering of the skin. These symptoms can be caused by one of two conditions called Toxic Epidermal Necrolysis (TEN) or Stevens Johnson Syndrome (SJS).

TEN and SJS are both serious conditions and could be life threatening. This happens in fewer than 1 in 100 people (1%).

Coping with side effects

We have more information about side effects and tips on how to cope with them.

Important information

Other medicines, foods and drinks

Drugs can interact with some other medicines and herbal products. Tell your doctor about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Many medicines, foods and herbal supplements can react with idelalisib. In particular medicines, foods and herbal supplements which contain CYP enzymes. 

Loss of fertility

You may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.    

Contraception and pregnancy

This treatment might harm a baby developing in the womb. It is important not to become pregnant or father a child while you're having treatment and for a few months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and the shingles vaccine (Zostavax).

You can:

  • have other vaccines, but they might not give you as much protection as usual
  • have the flu vaccine (as an injection)

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Last reviewed: 
22 Oct 2018
  • Electronic Medicines Compendium 
    Accessed August 2018

  • Immunisation against infectious disease: Chapter 6: General contraindications to vaccination
    Public Health England
    First published: March 2013 and regularly updated on the Gov.UK website

  • PI3Kδ Inhibition by Idelalisib in Patients with Relapsed Indolent Lymphoma

    AK Gopal and others 

    New England Journal of Medicine, 2014. Vol 370, Issue 11, Pages 1008-1018

  • Idelalisib for the Treatment of Chronic Lymphocytic Leukemia

    M. Khan and others

    ISRN Oncology, 2014. Article ID 931858

  • LCA Haemato-Oncology Clinical Guidelines. Lymphoid Malignancies: Chronic Lymphocytic Leukaemia (CLL) and B-prolymphocytic Leukaemia (B-PLL)
    London Cancer Alliance West and South, 2015

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact with details of the particular issue you are interested in if you need additional references for this information.